FLEXIBLE SHEET MATERIAL

Abstract: A flexible sheet material suitable for use for example as body armour comprises a plurality of individual rigid plates (10) all lying in the same plane and each both interfitting and interlocking with its adjoining plates (10) by having interengaging waisted projections (11) and re-entrant recesses (14) on successive sides. The edge wall profile of each plate is shaped to co-operate with the edge wall profile (figure 2) of the adjoining plate whereby relative separation of those plates (10) in the direction normal to the general plane of the sheet material is resisted. The edge profile may be V-shaped, with the edge profile of the adjoining plate (10) complementary form, or the angle of the edge wall of one plate (10) may vary around the periphery of one plate (figures 3, 4a, 4b), with the edge wall profile of the adjoining plate (10) matching the edge wall angle of said one plate.

Description: FLEXIBLE SHEET MATERIAL This invention relates to a flexible sheet material. The invention will be described with particular reference to a sheet material suitable for use as a body armour, for example to resist penetration by a knife blade or a projectile. However, the flexible material may be used in a wide variety of other circumstances and for other purposes and should not be regarded as being limited to a material solely for use as a body armour. As society becomes more violent, increasing use is being made of body armour to protect the wearer against injury either from a knife attack or from a projectile fired from a firearm, air-pistol, cross-bow or the like. Such armour must be flexible to give the user freedom of movement and should be gas permeable to reduce condensation during protracted use. Body armour often is in the form of a garment made from or containing a material resistant to penetration and usually protects the torso, though other designs of body armour may protect the limbs as well. It is a reguirement of modern body armour to be relatively light weight and also relatively flexible. Moreover, it is often desirable for such material to be as unobtrusive as possible. It is an aim of the present invention to provide an improved material of this kind which may be manufactured relatively cheaply and which is also convenient to use whilst still able to give excellent protection properties. According to the present invention there is provided a flexible sheet material comprising a plurality of relatively rigid closely-juxtaposed discrete plates all lying in substantially the same plane when the material is laid out flat, the periphery of each of which plates both interfits and interlocks with the peripheries of each of the neighbouring plates and the edge walls of each plate co-operating with those of the neighbouring plates to resist relative separation of the plates in the direction normal to the general plane of the material. The sheet material of this invention has all the plates thereof lying in substantially the same plane and so not overlapping, unlike many previous designs of such materials. As such, the thickness of the material may be much reduced, so making it significantly easier to incorporate in a garment such as a vest or jacket. A part of the length of the periphery of one plate may have an edge wall profile of a convex or of a V- shape, and the part of the periphery of a neighbouring plate which interfits and interlocks therewith may have an edge wall profile of a complementary concave shape or of an inverted V-shape, as appropriate. In the case of a V-shaped profile, the edge walls may be defined by bevels which meet substantially on the centre plane of the thickness of each plate. Preferably, each plate is based on a polygon which, in the case of a two-dimensional sheet, may have an even number of sides. Provided that the polygon has a sufficient number of sides, then separation of the plates in a direction normal to the principal surfaces of a plate may be prevented by a part of the length of the periphery of one plate having an edge wall profile lying at an acute angle to one surface of the plate and another part of the length of the periphery lying at an obtuse angle to said one surface of the plate, the parts of the peripheries of the neighbouring plates which interfit and interlock therewith having their respective edge profile parts of complementary forms. Thus, the periphery of any one plate may have successive edge walls of the polygon on which that plate is based lying alternately at acute and obtuse angles, respectively. At a region where there is a transition between successive edge walls lying respectively at acute and obtuse angles, adjacent plates may be relieved to from an opening through the sheet material, preferably of circular shape. A plug may then be fitted in that opening, the plug having an enlarged head on each side of the sheet material, which head overlies the marginal regions of the plates around the opening. In the sheet material of this invention, each plate may have at least one plane of symmetry perpendicular to the surface of the plate but preferably each plate is of the same shape, in plan, as all of the other plates. It would be possible for the sheet material, when in its 'natural' position, to have a three-dimensional curvature. In this case, it may be advantageous to have plates of more than one polygonal shape, mixed together to give the reguired curvature - for example, a mix of hexagonal and pentagonal shapes. The interfitting and interlocking between the plates, to resist separation thereof in the plane of the plates, is preferably obtained by having waisted projections on the plates, which interlock with re¬ entrant recesses of a complementary form also formed in the plates, the plates being interlocked by the projections of one plate being received into corresponding recesses of neighbouring plates. Each plate may be formed from a substance appropriate for the purpose for which the sheet material is to be put. For example, the substance may be selected from titanium, aluminium, steel, a ceramic, a thermo-setting or thermoplastics material, a filled or reinforced thermo-setting or thermoplastics material, wood, laminated wood, and a composition of fibrous material and a resin system, or a combination of these substances. The surface of each plate which is expected to receive an impact may be given an appropriate finish to minimise the effect of that impact. For example, in the case of a sheet material made from titanium plates and intended to be resistant to penetration by a high velocity projectile, the surface of each plate which, in use, is intended to face outwardly may have a surface finish of valleys and ridges formed therein. This is likely to reduce the likelihood of an impacting projectile sliding across the surface. Other surface finishes may assist in distorting a projectile at the point of impact in such a way as to allow a reduction in the overall thickness of a piece of body armour. The plates may be made by a technigue adapted for the substance being worked to from the plates - for example, individually by an injection moulding process, or by cutting the plates from a sheet of material. In the case of cutting, this may be performed by a water cutting-jet, a laser cutter, an electron beam cutter, a sonic cutter or some other non-contact cutting process. Another possibility would be to manufacture each plate from two or more separate parts, each formed by a suitable process such as machining, casting or forging, and then welding or otherwise fusing the plate-parts together once a sheet has been assembled from a plurality of such plate-parts. Yet another possibility would be to form the plates from a sheet of material by an etching process or by chemically leeching the material of the sheet away from a joint region between two plates. According to a second aspect of this invention, there is provided a process for manufacturing a flexible sheet material of this invention as described above and including the step of cutting a relatively rigid sheet to form said interfitting and interlocking plates. Such a cutting step may be performed to furnish the plates interlocked together, without the individual plates being separated one from the others. Such a cutting step may be performed by one of the processes mentioned above. By way of example only, certain specific embodiments of this invention will now be described in detail, reference being made to the accompanying drawings, in which:- Figure 1 is a plan view of a first embodiment of a flexible sheet material of this invention; Figure 2 is a sectional view taken on line II-II marked on Figure 1; Figure 3 is a plan view on an alternative plate element for use in constructing a sheet material of this invention; Figures 4A and 4B are part sectional views on the plate of Figure 3, taken respectively on lines A-A and B-B; Figure 5 is a plan view on part of a sheet material consisting of a plurality of plates each as shown in Figure 3; Figure 6 is a plan view of a further embodiment of sheet material of this invention, utilising modified plate elements which are nevertheless generally as shown in Figures 3 and 4; Figure 7 is a cross-sectional view taken on line VII-VII marked on Figure 6; Figure 8 is a plan view of two moulded plate-parts which may be joined to form a single plate; and Figure 9 is a plan view on part of a sheet material made from a plurality of plates each of each has two plate-parts as shown in Figure 8, fused together. Referring initially to Figures 1 and 2 , there is shown a sheet material in the form of a co-planar layer of individual plates 10 each based on a rectangle (in plan view) but having a pair of necked projections 11 formed on one opposed pair of sides 12 and 13 and having a pair of re-entrant recesses 14 formed in the other opposed pair of sides 15 and 16. Each plate 10 is thus similar in form to a conventional jigsaw puzzle piece of a relatively non-complex shape. Two side walls 12 and 15 are bevelled from the top and bottom, so as to have an edge wall profile of a V-shape, the bevels meeting on the centre plane 17 of the thickness of the plate and being formed at substantially the same angle to the planes of the top and bottom surfaces 18 and 19 of the plate. The other two side walls 13 and 16 are formed in a complementary manner to the side walls 12 and 15, and thus these side walls also have a V-shape, but inverted so that the top and bottom surfaces of the plate project further than the material of the plate at the centre plane of the thickness of the plate. An assemblage of plates as described above reguires at least three different designs of plate, ignoring plates at the edge region of the sheet, all similar but differing detail insofar as the edge wall profile of one side of a given plate has to match the edge wall profile in a complementary manner of the side of the next adjacent plate with which the side of the first-mentioned plate interfits and interlocks. It will be appreciated that a sheet material consisting of a plurality of identical plates each of which is as described above and all interlocked so that the necked projections are located in a corresponding re-entrant recess on the next adjacent plate, cannot be separated provided that the clearances between the plates are sufficiently small. The interlocking of the necked recesses and re-entrant recesses serves to prevent separation of the plates in the plane of the sheet material; and the interfitting of the projecting and inverted V-shaped side walls prevents separation of the plates in the direction normal to the surfaces of the plates. The clearances must be very closely controlled, in order to achieve the interlocking and separation- resistance described above. Clearly, if the clearances between the profiles of two adjacent plates, respectively on a side having a necked projection and on a side having a re-entrant recess, are such that the projecting V-shaped side may slide past the top or bottom surface of the next adjacent plate, interlocking will not be achieved. Thus, the clearance K between adjacent plates must be less than dimension A, as marked on Figure 2. In order that the sheet material may display flexibility and so have the capability of being curved in at least two dimensions, there must be a minimum clearance between the plates in order to allow each plate to move slightly out of a strictly co-planar disposition, with respect to its neighbouring plates. By way of example, in a typical sheet material of this invention of the kind illustrated in Figures 1 and 2, the material has a nominal thickness of about 6 mm, the length of each side of the rectangle on which each plate is based may be about 15 mm and the projection of the centre plane on sides 12 and 15 beyond the top and bottom surfaces 18 and 19 of the plate (dimension A) is about 3 mm. For such a configuration, and in order to allow the material to be flexed through a radius of 50 mm without deforming the plates, the clearance K between the plates must be not less than 0.24 mm - but in order to give adequate security of interlocking, should be at least 50% less than dimension A. There are two ways in which the sheet material described above may be manufactured. In the first, the material is formed as two separate sheets each consisting of a plurality of essentially identical (in plan view) plates, but with the edge walls defined by cuts extending right through the material and lying at a non-perpendicular angle to the surface of the sheet. The angle of cut of any one edge of a given plate in one sheet is in the opposite sense to the angle of cut of the corresponding edge of the corresponding plate in the other sheet. Then, by bonding the two sheets together with the respective plates thereof exactly overlying one another, the combined plates will thereafter be interlocked against separation in all directions. The two sheets may be manufactured either by individually forming plates and then assembling those plates together; or the plates may be formed by cuts made in a sheet of material without those plates being separated one from another, provided that the cutting can be performed with a sufficiently high degree of accuracy and with a sufficiently narrow kerf. In a second manufacturing process, a single sheet of material is cut from both sides to form the individual plates, the cutting being performed so that the two cuts meet on the centre plane of the sheet and the cutting device performing the cutting in such a way that the cut edges have the V-shaped profiles, shown in Figure 2. Such cutting may be performed by means of a water cutting process, where an extremely fine jet of water is fired at the sheet, under a very high pressure and in a highly controlled manner, or by a laser cutting process. Such cutting processes are known and understood in the art and form no part of the present invention; they will not therefore be described in any detail here. Figures 3 to 5 show an alternative design of sheet material utilising the principles described above with reference to Figures 1 and 2. Here, each individual plate 20 is based on a hexagon and the side edges are cut in such a way that the plates are all identical and yet the material comprised by the plurality of interlocking plates displays the same characteristics as have been described above. In Figure 3, the hexagon on which the plate is based is shown by lines 21 to 26 inclusive and it can be seen that the sides of the plate alternately have necked projections 27 and re-entrant recesses 28, of complementary forms. This plate profile allows adjacent plates to interlock as shown in Figure 5 and separation of the plates in the plane of the material is resisted by the projections and recesses 27 and 28 respectively interlocking. Separation in a direction normal to the plane of the material is resisted by the profile of the edges of each plate, which, on the adjacent interlocking portions, are of complementary forms. Figure 4A shows the profile of the edge portions of the plates on those sides which are provided with the necked projections 27 and it can be seen that these are cut with an obtuse angle a between the top face 29 and the side edge 30; on Figure 3, these edges are marked with the symbol +. Figure 4B shows the profile of the edge portions of the plates on those sides which are provided with the re-entrant recesses 28 and it can be seen that these are cut with an acute angle (3 between the top face 29 and the side edge 31, with the relationship (or + β) = 180°; on Figure 3, those edges are marked with the symbol -. The transitional edge regions between those indicated with + and - symbols extend essentially perpendicularly to the faces of the plate, and are marked with the symbol o. As with the previous embodiment, the clearance between adjacent plates must be sufficient to allow the material to be flexed out of a strictly co-planar configuration, but the clearance must be less than (t/tan β) where t is the thickness of the plate material. A typical embodiment of sheet material as shown in Figures 3 to 5 may consist of a polyester or epoxy resin system reinforced with aramid fibres. The side of the hexagon on which each plate is based may be in the range of 5 to 25 mm with the material thickness being about 6 mm. Conveniently, the plates are cut from a piece of the material without the plates being separated therefrom, for example by means of a high pressure water jet cutting technique or by laser cutting, as has been mentioned above. Referring now to Figures 6 & 7, there is shown another embodiment of sheet material of this invention, constructed from a modified form of plate. Each of the plates 35 is generally similar to the plates 20 of the embodiment shown in Figures 3 and 4 and so will not be described again in detail here. However, at each corner region of each plate, which region has been marked with the symbol o in Figure 3, the material of the plate has been cut away at 36 so that three adjoining plates together define a circular hole extending through the thickness of the material. In each hole, there is located a rivet 37 having an enlarged rounded head 38 on each side of the sheet material, which rivet 37 is a lose fit in the hole, as illustrated in Figure 7. In the case of plates made of titanium, for example, the rivets may also be made of the same material, or could be made from hardened steel. Figure 8 shows two separate plate-parts 40 and 41 which are manufactured separately but which may be joined together by a fusion technique so as to form a complete plate similar to that shown in Figure 3. Such plate-parts may be manufactured by machining, casting or forging techniques from suitable materials, so as to have appropriate edge profiles, as has been described above with reference to Figures 3 and 4. A plurality of the plate-parts may be assembled together as shown in Figure 8 and the two plate-parts of each plate are then welded or otherwise fused together along lines 42, for example by a laser welding technique, so as to form a complete, flexible sheet material of this invention. Provided that the welding is properly performed, the finished sheet material displays essentially the same characteristics as the material of Figure 5, consisting of plates 20 (Figure 3).

Claims: CLAIMS 1. A flexible sheet material comprising a plurality of relatively rigid closely-juxtaposed discrete plates all lying in substantially the same plane when the material is laid out flat, the periphery of each of which plates both interfits and interlocks with the peripheries of each of the neighbouring plates and the edge walls of each plate co-operating with those of the neighbouring plates to resist relative separation of the plates in the direction normal to the general plane of the material. 2. A flexible material as claimed in Claim 1, wherein a part of the length of the periphery of one plate has an edge wall profile of a convex shape and the part of the periphery of a neighbouring plate which interfits and interlocks therewith has an edge wall profile of a complementary concave shape. 3. A flexible material as claimed in Claim 1, wherein a part of the length of the periphery of one plate has an edge profile defined by bevels to have a generally V-shape and the part of the periphery of a neighbouring plate which interfits and interlocks therewith has an edge wall profile of a complementary inverted V-shape. 4. A flexible material as claimed in Claim 1, wherein a part of the length of the periphery of one plate has an edge wall profile lying at an acute angle to one surface of the plate and another part of the length of the periphery lying at an obtuse angle to said one surface of the plate, the parts of the peripheries of the neighbouring plates which interfit and interlock therewith having their respective edge wall profile parts of complementary forms. 5. A flexible material as claimed in Claim 4, wherein the periphery of any one plate has successive edge wall parts lying alternately at acute and obtuse angles respectively. 6. A flexible material as claimed in Claim 4 or Claim 5, wherein each plate has at least one plane of symmetry perpendicular to the surface of the plate. 7. A flexible material as claimed in Claim 6, wherein each plate is of the same shape, in plan, as all of the other plates. 8. A flexible material as claimed in any of the preceding Claims, wherein each plate is based on a polygon having an even number of sides, the sides alternately having a waisted projection and a re¬ entrant recess of complementary forms, the plates being interlocked against relative movement in their common plane by the projections of one plate being received into the corresponding recesses of neighbouring plates and said one plate receiving in its recesses the projections of neighbouring plates. 9. A flexible material as claimed in Claim 8, wherein each plate is based on a six-sided polygon. 10. A flexible material as claimed in any of the preceding Claims, wherein each plate is made of a material selected from: titanium, aluminium, steel, a ceramic, a thermo-setting or thermoplastics material, a filled or reinforced thermo-setting or thermoplastics material, wood, laminated wood, and a composition of fibrous material and a resin system. 11. A flexible material as claimed in any of the preceding Claims, wherein the region of a junction between three or more plates is apertured, a loose plug being fitted in the aperture. 12. A process for manufacturing a flexible material as claimed in any preceding Claim, including the step of cutting a relatively rigid sheet to form said interfitting and interlocking plates with the plates interlocked together, without the individual plates being separated one from the others. 13. A process as claimed in Claim 11 wherein the sheet is cut by a water jet or laser cutter.

Inventors: PATCHETT KIM, PATCHETT, KIM
Applicants: PATCHETT KIM, PATCHETT, KIM
Application year: 1994
Main classification: A41D31
IPC codes: A41D13, A41D31, F41H1, F41H5